Which type of strata is rare in occurrence?

Type of hydropower tunnel where water is conveyed under high pressure to turbines is ______

Tunnels associated with hydropower generation are called ______

Geologically, how many classes of tunnels are recognized?

In synclinal condition, low pressure areas are found at ______

What occurs due to falling of big rock blocks or sides due to release of stresses during tunnelling?

Layers dipping at angles up to 45° may be called ______

Type of hydropower tunnel where water is conveyed under gravity is ______